SCA 12: Eurographics/SIGGRAPH Symposium on Computer Animation

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https://diglib.eg.org/handle/10.2312/424

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Browsing SCA 12: Eurographics/SIGGRAPH Symposium on Computer Animation by Subject "I.3.5 [Computer Graphics]"

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    Energetically Consistent Invertible Elasticity
    (The Eurographics Association, 2012) Stomakhin, Alexey; Howes, Russell; Schroeder, Craig; Teran, Joseph M.; Jehee Lee and Paul Kry
    We provide a smooth extension of arbitrary isotropic hyperelastic energy density functions to inverted configurations. This extension is designed to improve robustness for elasticity simulations with ex- tremely large deformations and is analogous to the extension given to the first Piola-Kirchoff stress in [ITF04]. We show that our energy-based approach is significantly more robust to large deformations than the first Piola-Kirchoff fix. Furthermore, we show that the robustness and stability of a hyper- elastic model can be predicted from a characteristic contour, which we call its primary contour. The extension to inverted configurations is defined via extrapolation from a convex threshold surface that lies in the uninverted portion of the principal stretches space. The extended hyperelastic energy den- sity yields continuous stress and unambiguous stress derivatives in all inverted configurations, unlike in [TSIF05]. We show that our invertible energy-density-based approach outperforms the popular hy- perelastic corotated model, and we also show how to use the primary contour methodology to improve the robustness of this model to large deformations.
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    Faster Acceleration Noise for Multibody Animations using Precomputed Soundbanks
    (The Eurographics Association, 2012) Chadwick, Jeffrey N.; Zheng, Changxi; James, Doug L.; Jehee Lee and Paul Kry
    We introduce an efficient method for synthesizing rigid-body acceleration noise for complex multibody scenes. Existing acceleration noise synthesis methods for animation require object-specific precomputation, which is prohibitively expensive for scenes involving rigid-body fracture or other sources of small, procedurally generated debris. We avoid precomputation by introducing a proxy-based method for acceleration noise synthesis in which precomputed acceleration noise data is only generated for a small set of ellipsoidal proxies and stored in a proxy soundbank. Our proxy model is shown to be effective at approximating acceleration noise from scenes with lots of small debris (e.g., pieces produced by rigid-body fracture). This approach is not suitable for synthesizing acceleration noise from larger objects with complicated non-convex geometry; however, it has been shown in previous work that acceleration noise from objects such as these tends to be largely masked by modal vibration sound. We manage the cost of our proxy soundbank with a new wavelet-based compression scheme for acceleration noise and use our model to significantly improve sound synthesis results for several multibody animations.
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    Linear-Time Smoke Animation with Vortex Sheet Meshes
    (The Eurographics Association, 2012) Brochu, Tyson; Keeler, Todd; Bridson, Robert; Jehee Lee and Paul Kry
    We present the first quality physics-based smoke animation method which runs in time approximately linear in the size of the rendered two-dimensional visual detail. Our fundamental representation is a closed triangle mesh surface dividing space between clear air and a uniformly smoky region, on which we compute vortex sheet dynamics to accurately solve inviscid buoyant flow. We handle arbitrary moving no-stick solid boundaries and by default handle an infinite domain. The simulation itself runs in time linear to the number of triangles thanks to the use of a well-conditioned integral equation treatment together with a Fast Multipole Method for linear-time summations, providing excellent performance. Basic zero-albedo smoke rendering, with embedded solids, is easy to implement for interactive rates, and the mesh output can also serve as an extremely compact and detailed input to more sophisticated volume rendering.
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    Long Range Attachments - A Method to Simulate Inextensible Clothing in Computer Games
    (The Eurographics Association, 2012) Kim, Tae-Yong; Chentanez, Nuttapong; Müller-Fischer, Matthias; Jehee Lee and Paul Kry
    Inextensibility is one of the most fundamental properties of cloth. Existing approaches to handle inextensibility often require solving global non-linear systems and remain computationally expensive for computer game uses. Real time performance can be achieved by allowing damping or stretching at reduced solver costs, but these compromise visual realism - the cloth either looks stretchy or fine wrinkles get lost. Our long range attachment (LRA) method exploits that typical game character clothing tends to be attached to some kinematic parts of the character. LRA method applies unilateral distance constraint between free particles of the cloth to distant attachment point on the character, preventing them from stretching away from the kinematically driven attachments (e.g. shoulder for a cape). This simple step provides an efficient shortcut for enforcing global inextensibility that can be readily implemented into existing game physics methods such as PBD.
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    Smoke Sheets for Graph-Structured Vortex Filaments
    (The Eurographics Association, 2012) Barnat, Alfred; Pollard, Nancy S.; Jehee Lee and Paul Kry
    Smoke is one of the core phenomena which fluid simulation techniques in computer graphics have attempted to capture. It is both well understood mathematically and important in lending realism to computer generated effects. In an attempt to overcome the diffusion inherent to Eulerian grid-based simulators, a technique has recently been developed which represents velocity using a sparse set of vortex filaments. This has the advantage of providing an easily understandable and controllable model for fluid velocity, but is computationally expensive because each filament affects the fluid velocity over an unbounded region of the simulation space. We present an alternative to existing techniques which merge adjacent filament rings, instead allowing filaments to form arbitrary structures, and we develop a new set of reconnection criteria to take advantage of this filament graph. To complement this technique, we also introduce a method for smoke surface tracking and rendering designed to minimize the number of sample points without introducing excessive diffusion or blurring. Though this representation lends itself to straightforward real-time rendering, we also present a method which renders the thin sheets and curls of smoke as diffuse volumes using any GPU capable of supporting geometry shaders.